Crossing over from electromagnetic induced transparency (EIT) to Autler-Townes splitting (ATS) in a single superconducting fluxonium artificial atom.*

  Electromagnetically induced transparency (EIT) has been demonstrated in the atomic system, artificial atoms, and meta-structures. Previous demonstrations of EIT in superconducting artificial atoms involve coupling to other degrees of freedom such as resonators or other superconducting atoms. Here we report our design and experiment of the EIT with a single Fluxonium qubit inside a microwave waveguide. Because of large anharmonicity and tunability of the Fluxonium qubit, we designed a Lambda-type system with the controlling and probing transitions are strongly coupled to the transmission line while the transition between |0> and |1> states are protected while the fluxonium qubit close to the sweet spot. We observed a cross over from EIT to Autler-Townes splitting (ATS) regimes by tuning the controlling drive power. We further use Akaike information criterion (AIC) to identify the transition from EIT to ATS regime. The experimental results also agree with prediction of a three-level system’s model. This hardware efficient device can be used for slow light and quantum memory in microwave regime.